1. Field of the Invention
The present invention relates to a head-up display system which allows, for example, the driver of a car to view a vehicular information, while looking out a front windshield of the car, by projecting the vehicular information in the direction of the front windshield.
2. Description of the Prior Art
Hitherto, various head-up display systems have been proposed. For example, a reflection film has been proposed to be install on a windshield of a car or of an airplane to reflect light rays carrying images of vehicular information. As to the position of the reflection film relative to the windshield, it has been proposed to be directly fixed on the inboard surface of the windshield, to be interposed between two laminated glass sheets of the windshield, or to be put before the windshield. However, an image of a dashboard tends to be undesirably reflected by the reflection film and thus is viewed by the driver due to its high reflectance. This lowers the display quality of the head-up display system.
As another example, holography technique has been proposed to be used in the head-up display system. However, if this technique is used, it is necessary to employ a complicated optical device. Furthermore, there are unsolved problems such as image distortion and chromatic aberration.
As another example, it has been proposed to reflect light rays from the surface of a front windshield without using a reflection film. However, there is provided a problem of double image phenomenon or of ghost. To eliminate this problem, there are provided proposals such as JP-A-2-141720 and JP-A-2-294615. JP-A-2-141720 discloses a head-up display system having a phase film such as a .lambda./2 film. This film serves to rotate the plane of polarization of polarized light having a particular wavelength of .lambda.. JP-A-2-294615 discloses another head-up display system having a transparent birefringent film, for example, of polyethylene terephthalate. According to these proposals, the plane of polarization of polarized light having a particular wavelength can be rotated by 90 degrees so as to eliminate the double image problem. However, the plane of polarization of polarized light having a wide range of wavelengths can not be rotated by these proposals.